The invention relates to an open end friction spinning machine with two rollers driven in the same rotational direction and arranged adjacent one another to form a yarn forming wedge slot. Individual fibers of opened fiber material are supplied to the wedge slot by means of a fiber feed channel, the fibers being twisted into a yarn in the wedge slot and being drawn off in the longitudinal direction of the wedge slot. The transport of individual fibers is effected by means of a transport air stream flowing in the fiber feed channel which opens with its mouth at the wedge slot or at the cover surface of a roller. The transport air stream is created by means of one or several suction devices arranged in an extension of the fiber feed channel.
In an open end friction spinning device of the above-mentioned kind, disclosed in German published application (DE-OS) 29 43 063, one of the two friction rollers is formed as a so-called suction roller which exhibits a perforated cover surface and within which a suction insert is arranged, the effects of which suction insert are limited to the region of the wedge slot. The second friction roller exhibits a cylindrical closed circumferential surface. In this construction it is provided that the feed channel opens in a channel end part which extends approximately over the entire length of the wedge slot in the axial direction and at which an auxiliary suction device is connected which creates an air stream in the direction against the yarn withdrawal direction. The transport air stream inside of the fiber feed channel is essentially created by means of the suction inserts in the suction roller. The auxiliary air stream should effect that the total air stream and at least a part of the fibers traveling therewith change their movement direction to movement against the yarn withdrawal direction so that the binding together of all fibers should be improved. This auxiliary air stream against the yarn withdrawal direction must be very carefully controlled because the danger exists that especially short and light fibers are sucked off and not twisted into the yarn. This auxiliary air stream leads also to irregularities in the yarn form because the danger exists that the incoming fibers are twisted or buckled by engagement at the cover surface of the roller or at the existing yarn and are then tied or bundled in the buckled form.
The invention is based upon the problem to improve the fiber deposition for the yarn formation and to decrease the risk of fiber losses, especially of short and light fibers.
These problems are thereby solved by the invention by providing a suction device connected at the fiber feed channel in the region of its opening, which suction device creates an auxiliary air stream in the withdrawal direction of the yarn.
With this auxiliary air stream it is achieved that the forward ends of the extended incoming fibers are somewhat already turned in toward the withdrawal direction before they arrive at the wedge slot or the cover surface of the yarn being formed. In this manner the fibers are aligned toward the withdrawal direction without the danger of a buckling or the like occuring. Furthermore, the light fibers are totally turned toward the withdrawal direction and already in the region of the fiber feed channel mouth are brought into connection with the existing yarn so that they are bound or tied therein and are not sucked out of the unit.
In advantageous arrangements of the invention there is provided a suction opening in one of the bordering walls of the fiber feed channel at the withdrawal direction of the yarn wall side, which suction opening is connected with an underpressure (vacuum pressure) source. This suction opening facilitates the desired alignment of the front ends of the fibers inside of the mouth of the fiber feed channel. It is practically additionally provided that the underpressure at the suction opening is adjustable by means of an adjusting member. Thereby one can also meter/control the auxiliary air stream and especially so that it is suitable for the particular fiber material being spun.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.